Race officials decided to drop the last leg of the route between Anvik and Shageluk late Friday night after trail breaking crews encountered impassable conditions, said Iditarod executive director Stan Hooley.

''Most of the stretch between Anvik and Shageluk is very icy with no snow cover,'' Hooley said. ''There's really no way to navigate it.''

Race Marshal Mark Nordman said organizers immediately notified leading mushers, including Jeff King of Denali Park, Robert Sorlie of Norway, Ramy Brooks of Healy and defending champion Martin Buser of Big Lake. By Saturday morning, the remaining field of 56 mushers had been notified.

''The reaction has been great,'' Nordman said at the Anvik checkpoint, the new turnaround site of the race. ''I think the mushers trust me, so when I make a call saying this isn't safe, they say 'fine.'''

Meanwhile, King, a three-time Iditarod winner, and early front-runner Sorlie were vying for command of the lead.

King arrived first in Anvik at 4:21 a.m. Saturday and was taking his mandatory 24-hour layover after completing one of two eight-hour stops. Sorlie left the Eagle Island checkpoint at 5:06 a.m., completing his mandatory 24-hour layover. He pulled into Anvik at 1:59 p.m. and began an eight-hour stop there.

Although King had 14 dogs to Sorlie's 12, the Norwegian was happy to hear he would be able to leave six hours before King.

''I have control of the lead right now, he said.

Brooks, who has completed his 24-hour layover and an eight-hour stop, left Eagle Island 11:06 a.m. for the 60-mile run to Grayling, 18 miles north of Anvik. Buser, a four-time Iditarod winner, left Eagle Island at 12:58 p.m. He has completed his 24 hours and an eight-hour stop.

The 31st running of the Iditarod has already gone through unprecedented changes because of an unusually warm winter that forced organizers to change the traditional route and move the start north to Fairbanks.

The changes had extended the course 70 miles, to about 1,170 miles. From Fairbanks, mushers have followed a trail to Nenana, Tanana and other stops and will take a loop along the Yukon River from Grayling to Kaltag before following the usual route to the Norton Sound coast and on to Nome.

The latest change cuts about 50 miles from the modified route.

Now mushers will turn around in Anvik and return on the Yukon River to Kaltag instead of traveling from Anvik to Shageluk and back to Kaltag.

''At this stage of the game, we're prepared for anything,'' Hooley said.

For the first time in the history of the Iditarod, mushers will cross paths with rivals for the 140-mile stretch between Anvik and Kaltag -- a situation that could discourage laggers, some mushers said. On the other hand, race leaders will be the first to run against the wind that consistently sweeps across the Yukon River, Nordman said.

''Psychologically, it's no different than one musher arriving at a checkpoint just as another is leaving,'' he said. ''You know where they've been.''